1. Field of the Invention
The present invention relates to a platform incorporating at least one integrated transducer and to a method of producing the said platform. It is more particularly applicable to integrated magnetic heads for magnetic peripherals of data-processing systems, in particular disc memories.
2. Description of the Prior Art
In present day data-processing systems, use is more and more frequently being made of magnetic disc memories because of their storage capacity and the relatively short time taken by magnetic read/write heads to either store information on the discs or to access information contained anywhere on the discs from the moment when the heads receive an order to store or access this information from the said processing system.
Magnetic discs carry information on concentric circular recording tracks whose width, measured across the diameter of the disc, does not exceed a few hundreths of a millimeter. These recording tracks are situated on both faces of the discs. The discs are driven in rotation at constant speed by an electric motor and to enable information to be written or read, the magnetic heads are arranged at a distance of a few microns above either face of the discs. In current practice, it is usual for only one magnetic head to be associated with each face of the discs.
Rotation of the discs results in the existence of a cushion or compressed air between each head and the face of the disc associated with it. This cushion prevents the head from touching the disc and thus damaging it. The head is therefore said to "fly" above the face of the disc.
The present day trend in the development of magnetic discs with improved performance characteristics is to increase both the radial density and the longitudinal density of the information on the discs, the radial density being the number of tracks per unit length measured across the diameter of the disc and longitudinal density being the number of items of information per unit length measured circumferentially along a track.
An increase in radial density is feasible by reducing the width of the item of information and by the reduction, which the latter makes possible, in the width of the tracks. Similarly, a reduction in the length of an item of information makes it possible to increase longitudinal density. The width of the tracks and the length of an item of information are of the order of a few microns.
Low-cost magnetic heads are known which enable information to be read from and written onto magnetic discs on which both the radial and longitudinal densities are high. Typical are the integrated magnetic heads which are also known as integrated magnetic transducers. A magnetic head of this kind is described, for example, in French Patent No. 2,063,693, entitled "An Integrated Magnetic Head and a Method of Producing the Said Head" and its corresponding U.S. Pat. No. 3,723,665.
The head contains a magnetic circuit formed by two superimposed magnetic layers which are connected at one end while at the other end, which is close to the face of the disc which is associated with them, the layers are arranged substantially perpendicular to the face to form the pole-gap. The magnetic circuit also includes an electrical read and/or write winding between the magnetic layers formed from conductive layers which are superimposed in a direction perpendicular to the plane of the magnetic layers so that the latter form an envelope containing the conductive layers, which are separated from one another by electrically insulating layers.
An air-gap thus formed permits information to be read and written. The winding of the head generally has two, or even three, thin, stiff electrically conductive output strips which are connected by means of spot connections (spots of solder, for example) to flexible connecting wires equal in number to the strips which enable the winding to be connected electrically to the electrical read and write circuits of the disc memory.
As is described in French Patent No. 2,191,186 entitled "Improvements to Magnetic Heads and to their Mounting" corresponding to U.S. Pat. No. 3,846,841, the integrated head is embedded in a protective insulating material. The assembly formed by the head, the insulating material and the stiff, conductive output strips is covered further by an insulating layer, generally of the same kind as the substrate, which makes the stiff conductive output strips stronger mechanically. In other words, it can be said that this insulating layer is a member which provides protection for the said assembly and which supports the conductive electrical output strips mechanically. Because of its small size, it is possible to arrange a number of integrated magnetic heads on the same head-carrying platform so that they are all associated with the same face of a disc, an advantage of which is that it shortens the time taken by each head to access any item of information contained on this face. Such platforms are described, for example, in the above-mentioned U.S. Pat. No. 3,846,841.
In the majority of cases, the heads are mounted on two separate substrates one beside another, perpendicularly to the magnetic disc, and have a member for protecting them and mechanically supporting their conductive output strips which is common to them. This member also acts as a joint for the two substrates. Thus, the platform may be defined as being the assembly formed by the magnetic heads (together with their insulating material and their conductive electrical output strips), their substrates and their common protecting member. It is clear that a platform could be formed from a single substrate or from a number of substrates greater than two.
The platform so defined is generally, but not necessarily, in the form of a very shallow right-angled parallelepiped whose large faces are perpendicular to the plane of the heads, with what is termed the lower large face containing the pole-gaps of the heads and what is termed the upper large face containing the various spot connections to the conductive output strips from the head. To facilitate the description, this upper large face will be called the surface of the platform.
Together, the flexible connecting wires from each of the heads form a loop in the immediate vicinity of the surface of the platform. This has several disadvantages. For example, the loop interferes considerably with the "flying" of the head-carrying platform above the face of the magnetic disc which is associated with the heads.
Another disadvantage is that the read/write signals to and from the heads are upset by vibrations in the wires forming the loop. Further, when the disc memory contains a plurality of magnetic discs, the loop of wires takes up too much space, particularly in cases where the platform is located between two discs. Also, it should be apparent that the combination formed by the platform on the one hand and the loop of connecting wires on the other does not form a homogeneous whole structure from the point of view of its mechanical properties.
The present invention enables these drawbacks to be overcome by replacing, at the points where the spot connections to stiff conductive output strips are situated, the flexible connecting wires by stiff conductors formed by superimposing thin conductive layers deposited on the actual surface of the platform, which is roughened slightly.